Magnetic flowmeters powered by alternating current power supplies are well known. Such meters operate by measuring the voltage produced by a conductive fluid passing through a fixed diameter tube placed in an electrically generated magnetic field. The voltage produced is a linear function of volumetric flow rate through a fixed diameter tube according to Faraday's law of electromagnetic induction. These meters are extensively used in laboratory situations and mobile applications, such as when a meter mounted on a vehicle is taken to the site of a petroleum well and employed to measure additives used in a treating fluid for the well. In a laboratory setting, these flowmeters are used to measure and develop the well treatment additives. An example of such a flowmeter is the 1800 Series Magnetic Flowtube Lined Metal Metering Tube, produced by the Foxboro Company, Foxboro, Mass. Another such meter is described in U.S. Pat. No. 2,696,737 to E. Mittelman where the voltage induced as the fluid flows through a magnetic field is maximized. This allows for enhanced reading of the actual developed voltage and helps prevent the pickup of stray noise. Other relevant U.S. Patents are Kidwell (3,219,851), Hunter (3,323,364) and Seebode et al (3,926,049). Additionally, United Kingdom Patent specification No. 1,014,754 and an article entitled "Development of an Electromagnetic Water Current Velocity Meter" by Charles S. Hindes describe flowmeters which operate when a fluid flows through a magnetic field and induces a voltage proportional to the velocity of the fluid.
None of the aforementioned prior art discusses or addresses the problem solved by the present invention, which is specifically, expanding the range of fluid flow volumes over which a magnetic flowmeter can reliably and accurately operate. The limiting factor of a magnetic flowmeter range is the minimum flow velocity required to maintain an acceptable signal level. Prior to the present invention, a complete, separate flowmeter must be used for each of various fluid flow ranges. Therefore, in a laboratory setting where a flowmeter may be used for many different applications, the present invention eliminates the need to have different sized meters to run various tests at different volumetric flow rates. A typical magnetic flow meter may cost as much as $3,500.00, and ten such meters having varying flow ranges are often required. The present invention can substantially decrease laboratory costs by allowing a single flowmeter to operate over the same range of fluid flow velocity at many different volumetric flow rates, in contrast to the prior art, wherein several flowmeters were required.